Sometimes there is more than one seller. I try to pick the company that is affiliated with Amazon then you know all your charges up front. Third parties can have extra shipping and duty charges.
Shopping at Amazon.com can be a little bit trickier than .ca since Free Shipping doesn't apply. Go check-out Swagbucks 101 on page 2 of this forum. There is a section there on Amazon.com which explains shipping, duties and how to search for what ships to Canada.